Experimental proof-of-concept of the effect of inlet geometry on excavation forces and their reduction for small-scale continuous excavators

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Future in situ resource utilisation (ISRU) lunar mission concepts will require mechanisms that allow the available feedstock–mainly the lunar regolith–to be extracted from the lunar surface. Such extraction techniques in the reduced gravity environment of the Moon will need to minimise excavation forces, due to mass restrictions for robotic landers/vehicles and the large financial implications of placing cargo onto Earth’s satellite. An investigation of necessary excavation forces, both horizontally as well as vertically, for small-scale continuous lunar excavation systems based on their geometric inlet shapes, cutting angles, and digging depths has been undertaken. The use of vibration to disaggregate lunar soil and to reduce the necessary forces is explored as a proof-of-concept. Tests performed in a large analogue testbed have shown that the optimisation of the cutting geometry is crucial, as it inherently influences the necessary forces or even prevents deeper cuts into the soil. Our experiments indicate that shallow cuts (low digging depth) into soil at shallow angles are beneficial, and that the piling up of large surcharge masses must be avoided. Critically, applying vibration to cutting edges seems highly beneficial, as the achievable force reductions of up to 50% in the tested conditions far outweigh the additional power requirements. To make these implications immediately applicable to a wider audience, an estimation of available traction forces for certain robotic vehicles based on their mass is added for comparison.